How many total games have you played? Your first 20-30 games or so in a season have higher LP gains/losses as the system estimates your correct MMR range. As you play more games, the average LP swing decreases to around 16-20.
Other things that impact LP gain/loss:
- MMR relative to the game. If you're the highest MMR in the game, you'll gain a little less per win, lose a little more per loss. Vice versa is also true.
- MMR relative to your tier. If your MMR is significantly higher than your tier, you'll gain more per win, lose less per loss as the system tries to get you in sync. Vice versa is also true.
Streaks have no direct effect on LP gain/loss except in how they affect your MMR.